A steam turbine is used to drive a machine and is provided with a turbine body having a rotatably supported rotor. The rotor is rotationally driven by supply of the steam as a working fluid to the turbine body. In the steam turbine, the steam supplied to the turbine body or the steam extracted from the turbine body flows through a steam flow passage. A regulating valve is provided in the steam flow passage, and a switching drive mechanism having a regulating valve regulates the opening and closing of the steam flow passage to regulate the flow rate of steam (e.g., see Patent Literature 1).
Moreover, the regulating valve is generally driven using a structure which opens and closes the regulating valve via a lever, to which one end of the regulating valve is fixed, using a hydraulic servo mechanism. Meanwhile, a structure which operates the lever using an electric actuator for the purpose of saving space is also known.
Moreover, as a function of a double safety device (Fail safe), a function of operating the lever, for example, using a biasing force of a tension coil spring to forcibly close the regulating valve during power failure and during breakdown of an electronic governor which controls the switching drive mechanism is also known.